Alternating-current voltammeter



June 22 19266 J. H. MILLER ALTERNATING CURRENT VOLT AMMETER Filed Oct. 1925 Patented June 22, 1926.

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JOHN H. MILLER, OF OAK PARK, ILLINOIS, ASSTGNOE T0 JEUELL ELECTRICAL IN- STRUT/TENT COMPANY, OF CEICAGO, ILLINOIS, A COBPGBATION 0F ILLENOIS.

ALTERNATING-CURRENT VOLTAMMETER.

Application filed October My invention relates to instruments for measuring the voltage and amperage of alternating currents, and especially to an instruiient which is readily adapted to measure either 01 these quantities.

The object of my invention is to provide an alternating current volt-ammeter in which the connections in the instrument itself need not be changed in order to convert it from a voltmeter to an ammeter, but such conversion can be accomplished by merely c ianging the external connections to the instrument.

A :turther object is to provide an alternat ing current volt-ami'neter having only three terminals.

A further object is to provide an alternating current v0ltammeter which is simple in construction and accurate in operation, and which can be cheaply manufactured.

Other objects will appear from the tollowing description, reference being made to the accompanying drawing, in which the iigure shows the instrument diagrammatically with parts of the casing broken away in order to clearly show the working parts. As an illustration of the utility 01": my invention, 1 may explain that in testing the current supplied to railway signal circuits it has been necessary, in the past, tor the inspector to carry two instruments with him in order to test the alternating current voltage and amperage. By using the instrument of my invention it is necessary "for him to carry only one instrument, with accompanying saving in labor and expense, and increasing the speed of testing. The instrument which I have invented is also very useful in electrical laboratories and, in fact,

wherever occasion arises to determine alternating current voltage and amperage.

Due to the simple construction of the instrument oi my invention, it can be manuiactured at a cost. considerably lowerthan the cost of the two instruments which it replaces.

I have shown and will describe my invention in connection with an instrument of the iron vane type. variously known also as; the moving iron or soft-iron type. This is a well known type of instrument in which the indicator is deflected by the force of repulsion between two pieces of iron or steel, which are magnetized by the current 5, 1925. Serial No. 60,414.

which is being measured passing through a coil of wire surrounding the vanes.

The instrument as diagrammatically shown, is mounted on a base 1 upon which a suitable case 2 is secured. A suitably calibrated st .ie 3 is fixed to the top of the case in parallel sgaced relation thereto so as to be visible through a glass covered aperture in the top or" the case, as is usual in this c..ass oi? instruments.

T he moving element consists of a pivotally mounted shaft i at the upper end or which the pointer 5 is rigidly secured. Also rigid with this shai t is the fan 6 which swings with suiiiciently small clearance in a closed damping chamber 7 as to absorb the rotative energy given to the shaft and render the resulting actions dead beat. The force tending to rotate the shaft 4 is the result of the magnetic repulsion between the vane 8, which is fixed relative to the base, and the vane 9, which is rigidly secured to the lower portion of the shatt 4. The vanes are surrounded by a coil 10 of insulated wire which is secured to the base and is electrically connectecr to the line in which the current is to be measured. A suitable adjustable stop 11 limits the motion of the pointer at its zero position. The usual spiral spring (not shown) is connected to the shatt and tends to rotate it toward the zero position in which the pointer engages the stop.

Thus far I have described only the parts of the meter which are well known in the art. My invention consists in the novel electrical connections by which I utilize the. parts of an instrument as above described to give an indication/oi either current or voltage.

To accomplish this result I provide a transformer consisting of core. 12 upon which is a primary winding 13 of a relatively few number of turns of insulated low resistance wire. One end of the primary winding 13 is connected to the common terminal or binding post C. the other end being connected to the terminal A. The transformer secondary winding 14 has a relatively great number of turns of fine insulated wire and consequent relatively high reactance. The ends of the. secondary winding 14: are connected to the ends of the coil 10, which should have a low reactance as ccnr pared with the reactance of the secondary flux, cause a proportional. current in he secondary winding 14: and the COll 10. The

current in the coil will ctifect the magnetization of the vanes 8 and 9 and cause the vane. S) to he repelled a distance which is a. function of th current passing throu h the coil 10., and therefore by proper graduation and calibration ot' the scale 8, the indication is made to read in amperes flowing; through winding;

0 determine voltage, connections are made to the terminals C id Since these terminals are connected to the ends of the coil. 10 the instrument will function as above descrihed. T he winding; 1%: l reaet-ancc eoinpa ed with tl 10 that the current p: ssing; th ugh it will he negligible. The resistance .5 cuts down the current passing; through the coil 10 to an amount com arahle to that flowing through the coil when the instruncnt is hei l an ammeter, so that by suitable graduation and. calibration of the scale 3 the indication will he in number oi. volts dillerence in potential between the terminals C and V.

It will thus be seen that the instrument functions equally well as an ammeter and a voltmeter without the. necessity of main inp; any changes in the internal connections of the pi rts of the instrument, hut hy merely changing the external conneetitms to the instrument.

it will he unde'stooiil that while 1 have described my invention in connection with the iron vane type of instriunent, it may he readily adapted to other type of instruments. The invention is *apahle oi wide variations and adaptation in other respects for use in di'tlerent enjhodiments without departure from the principles of the inven tion. I do not restrict myself in any unes- 'ial particulars hut- *hat- I claim and desire to secure ters Patent is;

1. In combination witlan alternating current measuring; instrument of the iron vane type having a coil for magnetizing; the vanes, a transformer core, a primary wind ing thereon connected at its ends to a. pair or tern'iinals secondary winding connected in a closed circuit in series with said coil, the reactance of th secondary winding heing very much higher than that of the coil, connections from one oi said terminals to one end of maid coil, and high resistance connections from a third terminal to the other end of said coil.

In com inatiom an alternating; current measuring; instrument having a. pair of conductors t1"ansmittinc electrical energy for actumti' said instrun'icnt, a transformer iaving pr. nary and secondary windings, a pair of connectors connecting each end O'li' said secondary winding; with a respective ('onductcn'. a connnon terminal, a voltage terniinal an amper: tcrininah a high resist ance connection an said voltage terminal to one said *onductors, a connection from said common terminal to the other of said conductors. and means for connectin the ends or s id primary winding; to saic I men terminal and saiC amperage terminal respectively.

In comh inition rith an instruu'ient havin;' a coil and. means for indicating the cirrent flowing through said. coil, a traumfloriner having); primary windingand a high reactance secondary winding a minal connected to one end of said primary winding. to one end of said secondary winding' and to one end or said coil, a second terminal connected to the other end of said primary winding, nd a third terminal connected through a. high res....tauce element to the other end or said secondary winding and to the other end of said coil, so that current may he measured by n'ialrinp; connection to the first and second termirals and voltage may he measured hy making connection to the first and third teri'uinals.

r. An alternating current volt-ammeter emnprisina an indicator, a coil, means to actuate said indicator in accordance with the current flowing through said coil, a 'rans former having 'n'imaiy and secondary vindngs, said secondary winding being: coniec-ted to said coil in a closed series circuit, i resistance means for connecting; said seevondaiy winding to an external circuit and means for connecting; said coil and resistance in series to an enter al cir uit.

in witness whereof. I hereunto subscribe my name this 2nd day of October, 1925,

JOHN H. hHLLER. 

